Putting the Burgess Shales in the Shade

Canadian Scientists Discover new source of Cambrian Fossils

A team of Canadian scientists have discovered a treasure trove of Cambrian fossils, including eight new taxa at a location high in the Canadian Rockies, just 25 miles from the famous Burgess Shale sites. This discovery may herald a new era in palaeontology as more Cambrian fossil sites may exist, many more than previously thought.

It was the famous American palaeontologist Charles Walcott, who first came across a profusion of fossils in shale beds, at the site that was to become known as the Burgess Shale. He found the fossils quite by accident as he walked along a high ridge in the Rockies. The date of his discovery was 31st August 1909, now a team of Canadian researchers exactly, one hundred and one years and one day later, have announced the discovery of a new fossil rich location that could put the Burgess Shale in the shade.

Burgess Shale fossils are so important, as not only are the hard parts of organisms preserved, but in many cases evidence of soft tissues and actual body parts have also been preserved. Many palaeontologists regard the specimens from the Burgess Shale as the most perfectly preserved fossils from any geological period, quite an accolade as the strata dates from more than 500 million years ago.

It had been thought that the Burgess Shale fossils were unique and that no other locations would have the exact geological features that would have permitted such a large amount of fossil material to be preserved. With the discovery of this new fossil rich site, with its own exquisitely preserved specimens, just 25 miles from the original Burgess Shale location, many more such fossil rich areas may soon be discovered.

The creatures entombed in the Burgess Shale deposits inhabited a marine environment directly under a submarine cliff. Mudslides from this cliff buried these animals, but significantly the mud was low in oxygen. Rapid burial in a de-oxygenated environment led to a slowing down in the decomposition of body tissues. Often these tissues were permineralised (replaced by minerals) and consequently much better preserved.

Burgess Shale fossils actually occur in several locations, but they are all contained within a small area of the Rockies, around the little town of Field in Yoho National Park (British Columbia). All the fossils are found in strata belonging to the Stephen Formation, which in some parts is extensively exposed and represents deposits over 250 metres thick. However, a team of scientists led by palaeontologist Jean-Bernard Caron of the Royal Ontario Museum (Toronto) have reported finding Burgess-like fossils in the valley of the Stanley Glacier in Kootenay National Park. At this location, the Stephen Formation is exposed but in much thinner strips, no more than 160 metres thick.

Writing in the scientific journal “Geology” the team report that about 50% of the animal groups represented at the Stanley Glacier site have been found at other Burgess Shale locations, but in different abundances. This information will help the scientists to learn more about the evolution and diversity of Arthropods such as the Trilobites for example.

Trilobites were a highly successful Order of marine Arthropods, that arose in the Cambrian and eventually became extinct at the end of the Permian approximately 250 million years ago.

Commenting on this new site, Peter Allison, a geoscientist at Imperial College (London) stated:

“This new locality adds to our knowledge of the environments where these organisms lived and died and thus adds important context.”

Eight new taxa, previously unknown to science have also been unearthed. These new organisms include a new, as yet unnamed worm, a new member of the Anomalocarids, a predatory group of nektonic (actively swimming) predators and another type of Arthropod with primitive eyes on stalks that projected from its head shield.

The new Anomalocarid has been named Stanleycaris hirpex in honour of the Stanley Glacier. All these creatures inhabited an area of warm, equatorial sea just off the coast of the landmass known as Laurentia.

A Picture of a Typical Anomalocarid

Picture Credit: BBC Worldwide/Framestore

Anomalocarids were a group of predatory Arthropods, that have no extant relatives. Some of these marine hunters were up to ten times bigger than any other animal living at the time, with some specimens estimated to be approximately 2 metres long. They had large, rotund eyes on stalks and under the head, a circular shaped mouth with sharp interlocking plates that could crush the exoskeletons of Trilobites and other marine creatures. The curled front appendages had sharp spikes on them and scientists believe that these pincer-like organs were used to grab prey. The name Anomalocaris (pronounced An-oh-mal-low-kar-is) means “odd shrimp”.

The Stanley Glacier fossils were not formed in the presence of a submarine cliff. This suggests that creatures can be fossilised in amazing detail under other geological conditions, giving rise to the possibility of many more Cambrian fossil sites with soft body preservation being found.

The research team state:

“We consider it likely that future exploration and study will continue to yield new taxa from the “thin” Stephen Formation, which is exposed over a broader area regionally than the “thick” Stephen Formation.”